The technology disclosed relates to lab based over-the-air (OTA) testing of multiple antenna devices, and more particularly to techniques for OTA testing suitable for producing a test signal to emulate a wireless channel while using a limited number of transmit elements.
When designing over-the-air (OTA) testing approaches, channel modeling concepts are applied in order to insure that the received signal is representative of the desired test condition. Modern radio systems use different technologies including spread spectrum techniques such as wide-band code division multiple access (WCDMA), and orthogonal frequency division multiple access (OFDMA). These two technologies are significantly different in the way they process the received signal, leading to differences in how the RF channel is modeled. This impacts the design of an OTA test.
For wide band radio systems, the multi-path radio channel can be modeled as a series of delayed copies of the signal. For spread spectrum systems, such as WCDMA, each delayed copy of the signal that is resolvable within the radio bandwidth is called a path, and is typically characterized by a narrow angle spread. Each path is detected and may be processed or combined in a manner determined by the design of the receiver. Thus for this type of air interface, the paths are carefully specified to allow multiple antenna processing to be correctly emulated.
Use of predefined channel models can be used to define an OTA test. Recorded signals obtained from channel measurements can also be used in a play-back fashion to generate test signals.
Generating the test signals for an over-the-air test is complex. There are multiple paths. Each path must be constructed to produce the proper angle of arrival and angle spread in order to produce the proper correlation between antennas at the device-under-test. Thus, many individual transmit elements (also referred to as probes herein) would typically be required to be located in a variety of positions within an anechoic chamber to produce an adequate test signal. Having many probes is costly and complex to implement. Furthermore, having many probes will degrade the characteristics of the chamber due to additional reflections that may be produced.
Therefore, it is desirable to provide techniques for emulating real world conditions of a radio frequency signal reaching a device-under-test.